Irradiated synchronous rotor poles

In a previous paper, a model pole was described. The method of determining the Arrhenius Equation for this model was detailed. The equation was given for two different pole insulation systems. The maximum accumulated running time for a standby diesel-generator in nuclear service amounts to 8768 hours at a design hot spot of 130°C. Proof of qualified life requires the model to withstand an earthquake which is simulated by a shake table generating a vibratory force spectrum in the fully aged model. The ability to withstand a radiation dose is also desirable. Previous results showed that poles fully thermally aged at accelerated conditions using both insulations passed the seismic fragility test. In this paper, a number of fully aged poles were irradiated in a vendor´s facility with a dose of gamma radiation of 200 megarads from a Cobalt-60 source (dose rate 0.35 megarads/hr.). The poles showed a modest drop in insulation resistance. They were subjected to the severe seismic fragility evaluation and showed no evidence of failure. To evaluate synergistic effects, some new poles were recently sent for a 200 megarad dose which was followed by thermal aging and seismic evaluation. Results of the seismic test will not be ready until later, but the pole insulation was still good after 1392 hours at 160°C.